Mobile Data Usage

Is there any way to limit background mobile data usage? I have Wi-Fi available when I’m asleep, but when I’m awake, the app will randomly gobble up 3-4 megabytes of mobile data for no apparent reason. Tried using Datally to restrict this, and to disable all backup services during the day, but to no avail. Why would mobile data be consumed by this app when it is not actively being used?